Apparatus and systems requiring accurate time information may be for example, but not limited to, clocks, time of use utility meters, traffic lights; bus, train and plane scheduling apparatus; speed measuring instruments used in combination with global positioning satellite (GPS) devices, timers, parking meters, and the like. The market for low cost and sensitive radio frequency receivers for receiving time signals is enormous and current technology solutions are fairly expensive. Low frequency (LF) receivers may be used for self-setting clocks that receive the National Institute of Standards and Technology (NIST) WWVB time information and are used in high-end consumer and industrial applications. The cost of such receivers keep this technology out of the mass markets such as energy metering and lower end consumer electronics.
Various radio frequencies are used to transmit this time standard. The NIST radio station WWVB transmits at a very low frequency (VLF) of 60 kHz and effectively distributes standard time information to better than one second throughout the North American continent. Other VLF time standard transmitting sites are in the far east—JJY (Japan) and Europe—MSF (UK). NIST WWV also transmits time information in the high frequency (HF) radio spectrum.
The NIST radio stations (e.g., WWV, WWVH, WWVB) are continuously being used for both precise frequency and time calibration. The demand for precise frequency and time calibration is constantly growing as manufacturers continue to create new, lower cost products, in an effort to place “Atomic Time” in every home and office. However, acceptance of highly accurate and automatically set time appliances is greatly dependent upon cost and ease in implementation. Integrated circuit technologies have reduced the cost of time measurement, recording and display systems, e.g., digital clocks, parking meters, etc. However, complex and expensive receiving equipment is presently used to receive the time signals from the NIST radio stations. Existing low frequency radio time signal receivers are based upon high gain amplifiers with crystal filters to achieve good frequency selectivity, e.g., direct conversion receivers. The crystal filters are expensive and difficult to tune to a frequency that accurately coincides with the time signal frequency.
Therefore, what is needed is a low cost time signal receiver that receives time signals from the NIST radio stations and the like, and through time signal decoding makes the precise time available as decoded time information. In addition, it is desired that a low cost and sensitive time signal receiver may easily be fabricated in an integrated circuit.